Methyl Salicylate Increases Attraction and Function of Beneficial Arthropods in Cranberries

Chemical ecology in conservation biocontrol: new perspectives for plant protection

Threats to food security require novel sustainable agriculture practices to manage insect pests. One strategy is conservation biological control (CBC), which relies on pest control services provided by local populations of arthropod natural enemies. Research has explored manipulative use of chemical information from plants and insects that act as attractant cues for natural enemies (predators and parasitoids) and repellents of pests. In this review, we reflect on past strategies using chemical ecology in CBC, such as herbivore-induced plant volatiles and the push-pull technique, and propose future directions, including leveraging induced plant defenses in crop plants, repellent insect-based signaling, and genetically engineered crops. Further, we discuss how climate change may disrupt CBC and stress the importance of context dependency and yield outcomes.

Methyl salicylate improves the effectiveness of the odor-baited trap tree approach for adult plum curculio, Conotrachelus nenuphar (Coleoptera: Curculionidae), monitoring and attract-and-kill

In commercial apple orchards, the odor-baited trap tree approach involving the synergistic lure composed of benzaldehyde (BEN) and the PC aggregation pheromone grandisoic acid (GA) serves as an effective monitoring tool as well as an attract-and-kill strategy for plum curculio (PC), Conotrachelus nenuphar Herbst. (Coleoptera: Curculionidae), management. However, the relatively high cost of the lure and the degradation of commercial BEN lures by UV light and heat discourage its adoption by growers. Over a 3-yr period, we compared the attractiveness of methyl salicylate (MeSA), either alone or in combination with GA, to plum curculio (PC) with that of the standard combination of BEN + GA. Our main goal was to identify a potential replacement for BEN. Treatment performance was quantified using 2 approaches: (i) unbaited black pyramid traps (2020, 2021) to capture PC adults and (ii) PC oviposition injury (2021, 2022) on apple fruitlets of trap trees and of neighboring trees to assess potential spillover effects. Traps baited with MeSA captured significantly more PCs than unbaited traps. Trap trees baited with a single MeSA lure and 1 GA dispenser attracted a similar number of PCs as trap trees baited with the standard lure composed of 4 BEN lures and 1 GA dispenser based on PC injury. Trap trees baited with MeSA + GA received significantly more PC fruit injury than neighboring trees suggesting no or limited spill-over effects. Our collective findings suggest that MeSA is a replacement for BEN thereby cutting costs of lures by ca. 50% while maintaining trap tree effectiveness.

Deciphering Plant-Insect-Microorganism Signals for Sustainable Crop Production

Agricultural crop productivity relies on the application of chemical pesticides to reduce pest and pathogen damage. However, chemical pesticides also pose a range of ecological, environmental and economic penalties. This includes the development of pesticide resistance by insect pests and pathogens, rendering pesticides less effective. Alternative sustainable crop protection tools should therefore be considered. Semiochemicals are signalling molecules produced by organisms, including plants, microbes, and animals, which cause behavioural or developmental changes in receiving organisms. Manipulating semiochemicals could provide a more sustainable approach to the management of insect pests and pathogens across crops. Here, we review the role of semiochemicals in the interaction between plants, insects and microbes, including examples of how they have been applied to agricultural systems. We highlight future research priorities to be considered for semiochemicals to be credible alternatives to the application of chemical pesticides.

Components and composition of active volatiles attract on Diorhabda tarsalis (Coleoptera: Chrysomelidae) from Glycyrrhiza uralensis (Rosales: Leguminoseae)

Introduction

Perennial Chinese licorice, Glycyrrhiza uralensis, is an important medicinal plant. Diorhabda tarsalis, a leaf beetle, is a serious insect pest on the plant and cause serious yield losses every year and is attracted to healthy and pest-damaged licorice by plant volatiles.

Aim

The biologically active components of the volatiles released from G. uralensis have not been reported; the components of the volatiles that attract D. tarsalis need to be identified. Such compounds could potentially be used for monitoring and mass-trapping pests.

Methods

GC-EAD, GC-MS, EAG, Y-shaped olfactometer behavioral bioassays, and field trials were performed to identify the components and composition of active volatiles.

Results

Male and virgin female adults were generally attracted to volatiles from licorice, and volatiles from pest-infested plants were more attractive. Four compounds from licorice elicited a significant electrophysiological response (EAD) and were confirmed by EAG, including hexanal, (Z)-3-hexenal, (Z)-3-hexen-1-ol, and (E)-2-hexenal. With the exception of the (E)-2-hexenal, these molecules significantly attracted adults in individual behavioral bioassays, and a proportional mixture corresponding to beetle-damaged licorice of hexanal, (Z)-3-hexenal, (Z)-3-hexen-1-ol, and (E)-2-hexenal (8.78:15.26:57.24:18.72) was most effective for attracting D. tarsalis in the field, attracted a mean of 26 ± 7.19 beetles per trap.

Discussion

D. tarsalis was attracted to volatiles from healthy and herbivore-induced G. uralensis under both laboratory and field conditions. The aforementioned compounds show considerable potential for commercial application to monitor and control D. tarsalis populations.

Physiological Differences Between Seasonal Dimorphs of Agonoscena pistaciae (Hemiptera: Aphalaridae) Elicit Distinct Host Plant Responses, Informing Novel Pest Management Insights

We examined differences in the physiology and life history between dimorphs of the common pistachio psyllid, Agonoscena pistaciae (Burckhardt and Lauterer) (Hemiptera: Aphalaridae), and how they differ in elicitating host plant production of key metabolites and volatile compounds involved in the recruitment of herbivores and natural enemies. Summer morphs had higher activities of glutathione S-transferase, carboxylesterase, acetylcholinesterase, and cytochrome P450 monooxygenase, superoxide dismutase, catalase, peroxidase, phenoloxidase, and a higher total protein content compared to winter morphs, whereas the latter had higher amounts of lipid, carbohydrate, and glycogen. Winter morphs were heavier, with a higher chitin content and longer preoviposition period, but greater fecundity and longevity than summer morphs. A lower LC50 to thiamethoxam for winter morphs resulted in higher mortality following exposure to the recommended rate of this insecticide in a greenhouse trial. Feeding by winter morphs elicited more strongly the release of volatile compounds known to be attractive to other herbivores, whereas feeding by summer morphs elicited more strongly the release of volatiles implicated in the attraction of natural enemies. Feeding by psyllids increased the concentrations of nitrogenous compounds, carbohydrates, vitamins, and amino acids in plants, the winter morph eliciting larger changes and more improved host plant quality. We conclude that winter morphs are more vulnerable targets for chemical control in early spring, whereas management of summer morphs could rely more on conservation biological control.

Herbivory Protection via Volatile Organic Compounds Is Influenced by Maize Genotype, Not Bacillus altitudinis-Enriched Bacterial Communities

Belowground, plants interact with beneficial soil microbes such as plant growth-promoting rhizobacteria (PGPR). PGPR are rhizosphere bacteria that colonize roots and elicit beneficial effects in plants such as improved plant growth, pathogen resistance, abiotic stress tolerance, and herbivore protection. Treatment of plants with PGPR has been shown to trigger the emission of volatile organic compounds (VOCs). Volatile emissions can also be triggered by herbivory, termed herbivore-induced plant volatiles (HIPV), with important ramifications for chemical-mediated plant and insect interactions. Much of our current understanding of PGPR and herbivore-induced volatiles is based on studies using one plant genotype, yet domestication and modern breeding has led to the development of diverse germplasm with altered phenotypes and chemistry. In this study, we investigated if volatile emissions triggered by PGPR colonization and herbivory varies by maize genotype and microbial community assemblages. Six maize genotypes representing three decades of crop breeding and two heterotic groups were used, with four microbiome treatments: live or sterilized soil, with or without a Bacillus inoculant. Soil sterilization was used to delay microbiome establishment, resulting in low-diversity treatments. At planting, maize seeds were inoculated with PGPR Bacillus altitudinis AP-283 and grown under greenhouse conditions. Four weeks post planting, plants were subjected to feeding by third instar Helicoverpa zea (Lepidoptera: Noctuidae) larvae. Volatiles were collected using solid phase microextraction and analyzed with gas chromatography-mass spectrometry. Illumina NovaSeq 16S rRNA amplicon sequencing was carried out to characterize the rhizosphere microbiome. Maize genotype significantly influenced total volatile emissions, and relative abundance of volatile classes. We did not document a strong influence of microbe treatment on plant VOC emissions. However, inoculating plants with PGPR improved plant growth under sterile conditions. Taken together, our results suggest that genotypic variation is the dominant driver in HIPV composition and individual HIPV abundances, and any bacterial-mediated benefit is genotype and HIPV-specific. Therefore, understanding the interplay of these factors is necessary to fully harness microbially-mediated benefits and improve agricultural sustainability.

Methyl Salicylate Can Benefit Ornamental Pest Control, and Does Not Alter Per Capita Predator Consumption at Close-Range

Methyl salicylate (MeSA) is an herbivore-induced plant volatile widely tested for attracting natural enemies for pest control. MeSA is commercially sold as slow-release lures or as a spray. While MeSA application has increased the abundance of natural enemies in numerous food crops, its ability to reduce pests for crop protection is not as frequently demonstrated. Our first objective was to test MeSA lures in ornamental fields where few studies have been done, and monitor natural enemies, pests, and crop protection. A 2-year study in spruce container yards revealed more aphid parasitoids (Pseudopraon sp.), fewer aphids (Mindarus obliquus) on shoot tips, and less shoot tip damage in MeSA plots during the first year. A 2-year study in red maple fields revealed more predatory lady beetles and rove beetles, and parasitic Ceraphronidae, Diapriidae, and Chalcidoidea in one or both years with MeSA. Fewer pest thrips were also captured in MeSA plots, though it is not clear whether this was due to enhanced predation or reduced colonization. Maple growth as measured by stem diameter change did not differ with MeSA use. A 2-year study examining predation on sentinel Halyomorpha halys eggs in various mature ornamental stock blocks found no increase in predation except for 1 month, though green lacewings, lady beetles, and predatory thrips occurred more in MeSA plots in the first year. While MeSA is expected to enhance biological control by herding in natural enemies, the impacts that applied volatiles have on predator efficiency is mostly unknown. Thus, our second objective examined how volatiles would impact feeding rates at close-range. Adult carabid Pterostichus melanarius, adult coccinellids Coccinella septempunctata and Harmonia axyridis, and larval lacewing Chrysoperla rufilabris consumed their prey at similar rates in the presence/absence of MeSA when food was presented directly in a 28 cm2 or 30 ml arena, or when foraging in a 520 cm2 outdoor soil arena or 946 ml arena with aphids on leaves.

Methyl Salicylate Fails to Enhance Arthropod Predator Abundance or Predator to Pest Ratios in Cotton

Conservation biological control is a fundamental tactic in integrated pest management (IPM). Greater biological control services can be achieved by enhancing agroecosystems to be more favorable to the presence, survival, and growth of natural enemy populations. One approach that has been tested in numerous agricultural systems is the deployment of synthetic chemicals that mimic those produced by the plant when under attack by pests. These signals may attract arthropod natural enemies to crop habitats and thus potentially improve biological control activity locally. A 2-yr field study was conducted in the cotton agroecosystem to evaluate the potential of synthetic methyl salicylate (MeSA) to attract native arthropod natural enemies and to enhance biological control services on two key pests. Slow-release packets of MeSA were deployed in replicated cotton plots season long. The abundance of multiple taxa of natural enemies and two major pests were monitored weekly by several sampling methods. The deployment of MeSA failed to increase natural enemy abundance and pest densities did not decline. Predator to prey ratios, used as a proxy to estimate biological control function, also largely failed to increase with MeSA deployment. One exception was a season-long increase in the ratio of Orius tristicolor (White) (Hemiptera: Anthocoridae) to Bemisia argentifolii Bellows and Perring (= Bemisia tabaci MEAM1) (Hemiptera: Aleyrodidae) adults within the context of biological control informed action thresholds. Overall results suggest that MeSA would not likely enhance conservation biological control by the natural enemy community typical of U.S. western cotton production systems.

Interactive Effects of an Herbivore-Induced Plant Volatile and Color on an Insect Community in Cranberry

Simple Summary

Plants often increase their odor emissions after herbivore feeding damage, which in turn attract natural enemies of the herbivores such as insect predators. Synthetic versions of these so-called herbivore-induced plant volatiles (HIPVs) can be used to monitor populations of beneficial insects in agriculture. In addition, HIPVs can potentially attract the herbivores themselves. However, whether synthetic HIPVs interact with color to affect insect communities in farms is unknown. In this study, we tested a lure containing the HIPV methyl salicylate (named ‘PredaLure’) in combination with five different colored sticky traps to monitor insect populations in cranberry fields (also known as bogs). We found that hoverflies (also called flower flies or syrphid flies), whose larvae are predators of several insect pests including aphids and thrips, were attracted to PredaLure but this attraction was affected by the color of the trap. In fact, the numbers of hoverflies were 2–4 higher on yellow and white traps baited with PredaLure than on unbaited traps. Irrespective of trap color, plant-feeding thrips were also more attracted to PredaLure-baited than unbaited traps. Our study provides guidelines for the use of odor-baited colored sticky traps to monitor natural enemies such as hoverflies in an agricultural system like cranberries.

Abstract

Synthetic herbivore-induced plant volatiles (HIPVs) could be used to monitor insect populations in agroecosystems, including beneficial insects such as natural enemies of herbivores. However, it is unknown whether insect responses to HIPVs are influenced by visual cues, e.g., color. We hypothesized that the HIPV methyl salicylate (MeSA) interacts with color to affect insect captures on sticky traps. To test this, we conducted a 5 × 2 factorial field experiment in a commercial cranberry farm to monitor numbers of insect predators, parasitoids, and herbivores by using five colored sticky traps that were either baited with a MeSA lure (named ‘PredaLure’) or unbaited. At the community level, PredaLure increased captures of predators. At the individual-taxon level, captures of the hoverfly Toxomerus marginatus (Diptera: Syrphidae) and thrips (Thysanoptera: Thripidae) were higher on PredaLure-baited traps. However, only captures of T. marginatus on PredaLure-baited traps interacted significantly with color such that the numbers of this hoverfly on yellow and white traps were 2–4 times higher when baited with PredaLure. This study is the first to document the interactive effects of synthetic HIPVs and color on an insect community. Our findings have implications for optimal selection of HIPV-baited colored traps to monitor natural enemy populations in agroecosystems.

Metabolism of airborne methyl salicylate in adjacent plants

Salicylic acid (SA) and methyl salicylate (MeSA) are synthesized in many plants and are crucial components that establish their disease responses. The metabolism of airborne MeSA to SA has been previously reported. In this report, it was found that SA glucose ester (SAGE), ether (SAG), and salicyloyl-L-aspartic acid (SA-Asp) are metabolites of airborne MeSA. Furthermore, it was found that airborne MeSA was able to increase the endogenous amount of rosmarinic acid in Perilla frutescens, which is known as one of the functional components that contributes to the maintenance of human health.

Insect chemical ecology: chemically mediated interactions and novel applications in agriculture

Insect chemical ecology (ICE) evolved as a discipline concerned with plant-insect interactions, and also with a strong focus on intraspecific pheromone-mediated communication. Progress in this field has rendered a more complete picture of how insects exploit chemical information in their surroundings in order to survive and navigate their world successfully. Simultaneously, this progress has prompted new research questions about the evolution of insect chemosensation and related ecological adaptations, molecular mechanisms that mediate commonly observed behaviors, and the consequences of chemically mediated interactions in different ecosystems. Themed meetings, workshops, and summer schools are ideal platforms for discussing scientific advancements as well as identifying gaps and challenges within the discipline. From the 11th to the 22nd of June 2018, the 11th annual PhD course in ICE was held at the Swedish University of Agricultural Sciences (SLU) Alnarp, Sweden. The course was made up of 35 student participants from 22 nationalities (Fig. 1a) as well as 32 lecturers. Lectures and laboratory demonstrations were supported by literature seminars, and four broad research areas were covered: (1) multitrophic interactions and plant defenses, (2) chemical communication focusing on odor sensing, processing, and behavior, (3) disease vectors, and (4) applied aspects of basic ICE research in agriculture. This particular article contains a summary and brief synthesis of these main emergent themes and discussions from the ICE 2018 course. In addition, we also provide suggestions on teaching the next generation of ICE scientists, especially during unprecedented global situations.